ARM: dts: imx6q-tbs2910: avoid sdhci boot warnings

Avoid the following warnings (example for usdhc2):
/soc/aips-bus@02100000/usdhc@02194000: voltage-ranges unspecified
sdhci-esdhc-imx 2194000.usdhc: could not get ultra high speed state,
                               work on normal mode
sdhci-esdhc-imx 2194000.usdhc: No vqmmc regulator found

Signed-off-by: Soeren Moch <smoch@web.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>